WiTxrN recent years there has been a considerable advance on the technical side of production, and probably the most noticeable developments have been in the methods employed in artificially lifting the oil to the surface. However, as much progress has been made in the efficiency and methods used in handling flowing production, and it is this period of a well's, life, from the initial stages of its production until the time when artificial lift is applied, with which this article is concerned. This flowing period may be considered a well's most important phase; it is the cheapest type of production, and if adequately and scientifically controlled may be prolonged considerably. Also, by keeping accurate records of productions of gas and oil, pressures and oil analyses, the future type of artificial lifting facilities may be forecasted, the ultimate recovery of oil and the life of the well estimated.: The various classes of control to which a well is subjected may be divided into two main groups (1) Sub-surface control. (2) Surface control. The first covers the various factors existing in the formations, which give certain characteristics to one field and entirely different characteristics to another. The second is the mechanical control of the well, enabling efficient production of oil and gas from a given type of field.
The energy supplied to the oil. causing it to flow to the foot of a well .through the formation is initially in the form of pressure energy, and in some cases remains as such throughout the life of a field, the formation pressure being maintained. In such a case the field is said to be under hydraulic control. On the other hand, there is the type of field where the formation pressure starts to decline immediately the production of oil and gas commences, the relation between pressure and production being logarithmic. Such a field is said to be under volumetric control, and the energy supplied to the oil is derived from the expansion of the gas entrained with the oil.
Hydraulic Control.-In an oilfield under hydraulic control, as has been said, the formation pressure remains constant throughout the life of the field, and this pressure is maintained by the encroachment of, and final flooding of the field by water, giving to the oil a constant hydraulic head. If this formational pressure is great enough to flow wells initially, the wells will continue to flow throughout their lives, until water starts to be produced with the oil. At this point, due to the necessity of producing water with the oil, artificial lifting facilities may have to be employed, but the hydrostatic head may still be sufficient to flow the wells to the final point where the production becomes all water. Such a field, therefore, may be produced at very low costs, on account of the long flowing life, but this advantage may be partially offset by the treating cos